Microwave phase shifter system providing substantial constant phase shift over broad band



Sept. 27, 1966 N 1 K0 AN 3,275,952

MICROWAVE PHASE smFEli PROVIDING SUBSTANTIAL CONSTANT PH 5 T OVER BROAD BAND Fi May 29, 1950 ATTORNEY United States Patent This invention relates to microwave guide transmission systems and particularly to such systems that involve in their operation the determination and use of the phase relationships of waves in two Waveguide components of the system. More particularly, the invention relates to a wave transmission system having a constant phase shift over a wide frequency band.

In a conventional simultaneous lobing tracking radar system, energy from an oscillating source is fed to a simultaneous lobing horn antenna array through a single guide. Adjacent to and connected to the antenna array is a second guide that is slot-connected to the first guide. To compensate for the 90 degree shift in phase occurring at the slot coupling, a 90 degree phase shifter is inserted in the first guide between the slot and the antenna dipole. As a result, energy is radiated simultaneously from the antenna array in an overlapping lobal sum pattern.

When the reflected pulses are received back by the antenna array, the received energies pass from the separate dipoles through their two transmission guides until they reach the slot coupler, where the energy in each guide divides and part of the energy in each guide passes into the other guide. By suitably combining these outputs, sum and difference outputs can be formed. The difference output amplitude is proportional to the absolute error between the bearings of the target and the antenna while the sum output amplitude is relatively insensitive to this error. By comparing the sum and difference outputs using a phase detector, a D.-C. voltage can be obtained that has directional sense and which is proportional to the error. It is apparent that any phase errors introduced into the system by construction or electrical characteristics of the components of the guides and associated conduction current receiving apparatus will appear as a finite error and will reduce the operational efficiency of the system.-

One method of changing the phase relation between the waves of the two guides in the system is to make the guides of different lengths. However, if the operating frequency of the system is changed, a change in the guide wave length will be produced, which will cause a change in the phase relations.

Another method of changing the phase relation is by making the guides of the same length but of different dimensions, such that the guides have different guide wave lengths. In such constructions, .a change in the operating frequency of the system will cause a change in the phase relations of the waves in the two guides. However, the change in phase relation in this latter method is opposite in effect to the change when two similar guides of different lengths are used.

The present invention combines these two methods of obtaining a change in the phase relations of the waves in the two guides, with their opposing effects upon changes of the operating frequency of the system, and thereby produces a wide-band phase-delay circuit.

It will, of course, be understood that the invention is not limited in its application to a simultaneously lobing type of radar system, but is equally applicable to a wide variety of systems and their control and association circuits.

The principal object of the invention is to provide an arrangement of guide components in which the relative phase shift over two paths in the system is held constant.

3,275,952 Patented Sept. 27, 1966 ice Another object is to provide in a two path guide system a component to adjust the relative phase shift in the two paths.

Another object is to provide an arrangement of guide components in which the relative phase shift over the two paths in the system is held constant over a maximum frequency range.

Other objects and advantages of the invention will be apparent from the following detailed description made with reference to the accompanying drawings in which:

FIGURE 1 is a graph showing the relationship between the relative phase shifts in two guides of different linear lengths over .a range of free space wave lengths;

FIGURE 2 is a graph showing the relationship between the relative phase shifts in two guides with different cutoff Wave lengths, over a range of free space wave lengths;

FIGURES 3 and 4 are graphs showing the relationship between the relative phase shifts in two guides of different lengths and with different cut-off wave lengths over a range of free space wave lengths guides; and

FIGURE 5 is a cross-sectonal view of one preferred embodiment of the invention showing two waveguides in contact with each other and bent in the arcs of circles having a common center.

The wave length in a guide (k is known to be:

Substituting in Equation 2 the value of M in Equation 1,

0 i mm Differentiating 0 with respect to (Equation 4), the rate of change of phase shift with respect to the free space wave length becomes:

From Equation 2, the phase shift is shown to be proportional to l/ and from Equation 6 the rate of change of phase shift is shown to be proportional to M It is obvious that with the proper choice of 'values win in the parameters of these variables, different phase shifts may be obtained in two guides while the rates of change of these phase shifts may be held equal and the relative phase shifts may be held substantially at any value, say degrees, over a considerable band of frequencies. From the foregoing equations, in order for a pair of Waveguides of different lengths to have equal rates of change of phase shifts with change in operating wavelength at or near a mean operating frequency, the product of waveguide length and the propagation wavelength in the waveguide [for one should be equal to that product for the other.

To apply the invention to a particular guide system, it may be assumed that it is desired to hold the relative phase shift in two guides to 90 degrees over a certain band of wave lengths, greater than or less than a certain mean value. The relative phase shift for two guides of different lengths may be plotted over the desiredband of wave lengths.

The plots of these relationships result in a typical curve shown in FIGURE 1, in which the solid line 1 shows the relationship between relative phase shift and the free space wave length, for the mean relative phase shift value of 90 degrees (dotted line 2) and the mean of the free space wave length values (dotted line 3). Likewise the relationship between the relative phase shift and the free space wave length may be plotted (solid line) as in FIG- URE 2 for two guides with different cut-E wave lengths.

From the curves in FIGURES 1 and 2, the two relative phase shifts for two wavelength guides of different lengths and different cut-off wave lengths may be selected such that rates of change of phase shift in both of the guides are made equal over a definite band of Wave lengths.

The results of such selected or proportional lengths of guides and cut-off wave lengths values are shown in FIG- URE 3 in which the solid line 5 is for a positive wave Shltft and dotted line 6 is for a negative phase shift.

The curves in FIGURE 4 represent conditions corresponding to those represented in FIGURE 3, except that the guides have been selected in such proportion that the rate of change of relative phase shifts is slightly negative. Design of two guides with this characteristic is desirable when some component in the guide system causes a positive phase shift in the component with increases in the wave lengths of the radiation in the components.

In FIGURE 5 is shown a physical embodiment of a phase shifter of the invention. In the embodiment shown, the two guides 7 and 8 represent two parallel guides of width m, in which are being transmitted waves of wave length a and of relative phases p and If it is desired to shift the phase relation between the two transmitted waves, the two guides are bent beginning at positions in their length, such as shown by dotted line 9, into arcs of circles of such arc lengths, terminating at dotted line 10, such that 1 the linear length of the outer guide, minus 1 the linear length of the inner guide will equal the value of l, as defined in Equation 2. The difference in lengths of guides 6 and 7, (1), is shown as being obtained by bending the guides into arcs of circles having a common center. The difference in lengths of the guides however, may be obtained by other curved forms as long as the difference in lengths of'the guides equals the value of I selected to give the desired phase shift.

The device is made responsive over a wide frequency range by increasing the width of the outer guide, as at steps '11, from its normal width (m to a width 112 which increase in width changes the cut-off frequency of the guide and hence affects the phase shift of the Waves within the guide, as has been previously pointed out herein.

It is realized that the steps 11 in the outer guide may cause some reflections. In most practical applications of the invention, it has been found, these reflections can be neglected. However, should it be desired to eliminate these reflections, it may be done by introducing a short taper in the guides and thus eliminating the effects of the abrupt steps or a properly proportioned step may be introduced into the height of the guide.

-It will be seen that advantage is thus taken of two constructional transmission characteristics of guides that have opposite effects on the phase relations of the wave transmitted in the guides over a wide band of guide wave lengths and that by the selection of the forms and the 4 dimensions of the guides at wide-band phase shifter circuit is produced.

What is claimed is:

1. A microwave phase shifter providing a substantially constant phase shift over a wide frequency band comprising: a pair of waveguides of different lengths, one of said waveguides having a different cut-off wave length from that of the other, the product of the waveguide length and the wavelength in the waveguide at the mean operating frequency for one waveguide being equal to that product for the other, and means to apply radio wave energy at the operating frequency of predetermined relative phase relationship respectively at the ends of the two waveguides.

2. A microwave phase shifter providing a substantially constant phase shift over a wide frequency band comprising: a pair of waveguides of different lengths juxtaposed in the form of curves, one of which waveguides having a different cut-off wave length than the other, the product of the waveguide length and the wavelength in the waveguide at the mean operating frequency for one waveguide being equal to that product for the other, and means to apply radio wave energy at the operating frequency of predetermined relative phase relationship respectively at the ends of the two waveguides.

3. A microwave phase shifter providing a substantially constant phase shift over a wide frequency band comprising: a pair of waveguides having concentric axes and juxtaposed in concentric arcs about a common center, the lengths of said arcs having lengths differing in proportion to the desired phase shift between the waves in the respective waveguides, the cut-off wave length of the outer said waveguides being different from that of the inner of said waveguides, the product of the Waveguide length and the wavelength in the waveguide at the mean operating frequency for one waveguide being equal to that product for the other, and means to apply radio wave energy at the operating frequency of predetermined relative phase relationship respectively at the ends of the two waveguides.

4. A microwave phase shifter providing a substantially constant phase shift over a wide frequency band comprising: a pair of waveguides having concentric axes and juxtaposed in concentric arcs about a common center, the lengths of said arcs differing in proportion to the desired phase shift between the waves in the respective waveguides, the width of the outer of said waveguides being different from that of the inner of said waveguides, the

product of the waveguide length'and the wavelength in the waveguide at the mean operating frequency for one waveguide being equal to that product for the other, and means to apply radio wave energy at the operating frequency of predetermined relative. phase relationship respectively at the ends of the two waveguides.

5. A microwave phase shifter providing a substantially constant phase shift over a Wide frequency band comprising: a pair of waveguides having concentric axes and juxtaposed in concentric arcs about a common center, the lengths of said arcs differing in proportion to the desired phase shift between the waves in the respective waveguides, the width of the outer of said waveguides being different from that of the inner of said waveguides and the height of the outer of said waveguides being different from that of the inner of said waveguides, the product of the wave-guide length and the wavelength in the waveguide at the mean operating frequency for one waveguide being equal to that product for the other, and means to apply radio wave energy at the operating frequency of phase shift between the waves in the respective Waveguides, the outer of said waveguides being wider than the inner of said Waveguides and having steps substantially at the arcuate ends of said outer waveguide, the product of the waveguide length and the wavelength in the Waveguide at the mean operating frequency for one waveguide being equal to that product .for the other, and means to apply radio wave energy at the operating frequency of predetermined relative phase relationship respectively at the ends of the two waveguides.

6 References Cited by the Examiner UNITED STATES PATENTS 2,411,872 12/1946 Feldman et al 250-33.63

HERMAN KARL SAALBACH, Primary Examiner. 

1. A MICROWAVE PHASE SHIFTER PROVIDING A SUBSTANTIALLY CONSTANT PHASE SHIFT OVER A WIDE FREQUENCY BAND COMPRISING: A PAIR OF WAVEGUIDES OF DIFFERENT LENGTHS, ONE OF SAID WAVEGUIDES HAVING A DIFFERENT CUT-OFF WAVE LENGTH FROM THAT OF THE OTHER, THE PRODUCT OF THE WAVEGUIDE LENGTH AND THE WAVELENGTH IN THE WAVEGUIDE AT THE MEAN OPERATING FREQUENCY FOR ONE WAVEGUIDE BEING EQUAL TO THAT PRODUCT FOR THE OTHER, AND MEANS TO APPLY RADIO WAVE ENERGY AT 